This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
If the original contract is one which is required by law to be proved by writing, some courts hold that such a contract can not be modified by a subsequent oral executory contract.1 In other jurisdictions, the validity of a subsequent oral modification of such a contract depends upon the part of the original contract which it affects. As we have seen before,2 in many jurisdictions a memorandum under the statute of frauds need not show the consideration therefor, unless such consideration is an executory term of the contract. In such jurisdictions, an oral modification of a contract required by law to be proved by writing, is valid if it does not in any way affect the promise made by the party who is agreeing to do an act which brings the contract within such statute, but affects entirely the promise of an adversary party, which is the consideration for such promise. Thus, a written oil and gas lease, to be extended from year to year as long as production continues, upon a payment of specified royalty, may subsequently be so modified by parol as to discharge the lessee from liability as to such royalty.3 A written contract for the sale of land, which provides for the time of payment, may be modified by a subsequent oral contract, changing the time for making such payments. Thus, if the oral contract provides for the payment of certain monthly installments, and the delivery of the deed when the purchase price is paid in full, a subsequent oral contract to accept the rest of the purchase money with interest on deferred payments at once, gives the vendee a right to a deed for the property upon tender of such amount.4 A right to cut and use timber, which is created by a written contract, may be waived by an oral agreement.5
2 Malone v. Philadelphia, 147 Pa. St. 416; 23 Atl. 628.
3 Ede v. Knight, 93 Cal. 159; 28 Pac. 860.
1 Reid v. Plate-Glass Co., 85 Fed. 193; 29 C. C. A. 110; Burns v.
Peal Estate Co., 52 Minn. 31; 53 N. W. 1017; Rucker v. Harrington, 52 Mo. App. 481; Sanborn v. Murphy, 86 Tex. 437; 25 S. W. 610. 2 See Sec. 701 et seq.